I usually try to aim at a 66%/33% divide, crossing the line -slightly- if the ranged troops are villianese high chiefs or otherwise ranged troops that are highly capable in a melee. The black army assaulters and ravagers have good armor, decent ranged weapons and decent melee capacities for example. Similarly, serpent host soldiers combine ranged and melee often, like the khergit and zerrikan. I hate going up against Khergit for that reason. If I see 50 swadian sargeants, I know they'll stand there and swallow arrows, khergit lances shoot back - and hard, similarly with the nord troops, though they are better at melee due to their weapon choice.
So if I took the time to raise khergit, black army or nord armies, or when playing villianese, the garrisons may look very different than when I'm playing adenian side and use vaegir and elephant guard auxilliaries
so, it all depends.
though if I can staff a castle with 50 raven captains and 50 basilisk knights, I would be very happy.